Why do this? What are your goals? HST will make you stronger as your muscles get bigger. If your goal is simply functional strength for a sport or something, then do a whole body strength routine. If your goal is to put on some muscle and get stronger overall then do a full body HST routine. I don't see why you would split your training style by upper/lower body.
To sum up, HST will make you stronger everywhere, so you should probably just do full body HST. If you have a peculiar situation, then post how experienced you are with training and your specific personal training goals for better advice.